1. Field of the Invention
The invention relates to a helical-axial inducer/comminution device for solids-ladened fluid flow systems; and more particularly to an inducer/comminution device for a rotary kinetic pump in a fluid flow.
2. Background of the Invention
Many industrial processes involve the conveyance of fluid streams by centrifugal pumps. Often these fluid streams carry or contain solids, pieces of relatively solid material, that are too large to pass through the pump impeller passages or the passages in downstream process equipment. Rotary comminution devices are often utilized to reduce the size of solids to a size which can be passed by downstream pumps and equipment. Typically a solids-laden fluid stream is routed through an upstream rotary comminution device enroute to further processing.
The helical-axial comminutor is one such type of equipment that has been developed to reduce solids to a size that can be passed by pumps and downstream equipment. Another type of comminutor utilizes rotary radial cutter blades passing in close proximity to a stator to comminute solids. The problem with existing helical-axial and rotary comminutors is that they obstruct flow to the pump thereby creating the potential for cavitation in pump applications that have limited Net Positive Suction Head (NPSH) available to the pump.
When pumping fluids where NPSH availability is limited, helical-axial inducers are often applied to centrifugal pumps to boost pressure to the pump inlet so as to avoid cavitation. Inducers increase the pressure of the liquid at the impeller eye by accelerating liquid such that cavitation occurs on the inducer while meeting the impeller requirements for fluid flow. The sectional area normal to the meridional plane of an inducer throat is generally larger than that of the throat of the downstream impeller passage. The throat is defined as the section along the meridional axis with the smallest distance between any two opposing surfaces. Although inducers are effective at forestalling the onset of impeller cavitation, solids that pass through an inducer may still become lodged in the downstream impeller.
In summary, helical-axial inducers that are effective at reducing cavitation are not effective at solids reduction, and helical-axial and radial comminutors, although effective at solid size reduction, create a pump inlet obstruction to flow thereby increasing the likelihood of cavitation.